Oxygen sensor failures can lead to various emission pollutants exceeding standards, primarily including the following three major pollutants:
Increased Carbon Monoxide (CO) Emissions
When the oxygen sensor fails and causes a rich mixture, a large amount of carbon monoxide is produced. Under normal circumstances, the oxygen sensor accurately controls the air-fuel ratio around the theoretical value of 14.7:1, ensuring complete combustion of fuel. Once the sensor fails, the Engine Control Unit (ECU) cannot accurately adjust the fuel injection amount, leading to a rich mixture that results in incomplete combustion and a significant increase in carbon monoxide.
Excessive Hydrocarbon (HC) Emissions
Oxygen sensor failures can lead to a significant increase in hydrocarbon emissions. Whether the mixture is too rich or too lean, it will cause incomplete combustion, resulting in unburned hydrocarbons. When the oxygen sensor incorrectly indicates a lean mixture, the ECU increases the fuel injection amount, and the excess fuel cannot be completely burned; when it indicates a rich mixture, the ECU reduces the fuel injection amount, which also leads to incomplete combustion.
Increased Nitrogen Oxides (NOx) Generation
Oxygen sensor failures can also lead to excessive nitrogen oxide emissions. When the mixture is too lean, the combustion temperature rises, significantly increasing the generation of nitrogen oxides. Nitrogen oxides are one of the main causes of acid rain and photochemical smog, posing great harm to the environment and human health.
Specific Mechanisms of Emission Exceedance
Failure of Air-Fuel Ratio Control
The oxygen sensor monitors the oxygen content in the exhaust and provides feedback signals to the ECU, which precisely adjusts the fuel injection amount based on this information. When the sensor fails, the ECU cannot obtain accurate oxygen content information, leading to a failure in air-fuel ratio control, resulting in either a rich or lean mixture, which causes various pollutants to exceed standards.
Decreased Efficiency of the Three-Way Catalyst
Oxygen sensor failures can also affect the efficiency of the three-way catalyst. The three-way catalyst needs to operate near the theoretical air-fuel ratio to achieve optimal purification effects; once the air-fuel ratio deviates from the theoretical value, the catalyst’s ability to purify CO, HC, and NOx will sharply decline.
Exhaust Odor and Black Smoke
Oxygen sensor failures can also lead to exhaust odors and even black smoke. This is due to the increased emissions of harmful gases and particulates resulting from incomplete combustion, which not only affects the environment but may also cause the vehicle to fail environmental inspections.Therefore, timely inspection and replacement of faulty oxygen sensors are crucial for ensuring vehicle emissions meet standards, protecting the environment, and improving fuel economy.